The invention relates to a preparation suitable for preparing a neutral metal oxide sol.
Neutral titanium dioxide sols and processes for their preparation are described, for example, in EP 0,261,560. According to this specification, an acid titanium dioxide sol is neutralized by treatment with an anion exchanger resin. During this procedure, the neutralized sol shows a tendency toward agglomeration, which can be counteracted by stirring the sol vigorously for several hours. Another possibility for avoiding agglomeration comprises adding a water-soluble organic compound to the sol before or after the treatment with the anion exchanger, monomeric or polymeric polyalcohols, such as, for example, glycerol, ethylene glycol or polyvinyl alcohol, being proposed in particular for this process in EP 0,261,560.
Neutral metal oxide sols are used in many instances in industry. Thus, for example, neutral metal oxide sols can be mixed with polymers or used as binders for certain catalysts. Because of their good skin tolerance and their high absorption in the UV range, neutral titanium dioxide sols have been proposed for cosmetic uses, and in particular for sunscreen cosmetics.
However, the neutral metal oxide sols described to date are often characterized by a storage stability which does not meet all requirements adequately. The metal oxide sols to date furthermore often have a relatively low concentration of typically not more than 10-25% by weight; thus, for example, a titanium dioxide sol of a maximum of about. 25% strength is obtained in EP 0,261,560 by heating a dilute neutral titanium dioxide sol. For many applications, such as, for example, for the preparation of cosmetics, however, more highly concentrated sols are desired.